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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Christoph Paasch <christoph.paasch@gmail.com>,
	Eric Dumazet <edumazet@google.com>
Cc: "David S . Miller" <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jonathan Looney <jtl@netflix.com>,
	Neal Cardwell <ncardwell@google.com>,
	Tyler Hicks <tyhicks@canonical.com>,
	Yuchung Cheng <ycheng@google.com>,
	Bruce Curtis <brucec@netflix.com>,
	Jonathan Lemon <jonathan.lemon@gmail.com>,
	Dustin Marquess <dmarquess@apple.com>
Subject: Re: [PATCH net 2/4] tcp: tcp_fragment() should apply sane memory limits
Date: Mon, 17 Jun 2019 19:28:01 -0700
Message-ID: <03cbcfdf-58a4-dbca-45b1-8b17f229fa1d@gmail.com> (raw)
In-Reply-To: <CALMXkpYVRxgeqarp4gnmX7GqYh1sWOAt6UaRFqYBOaaNFfZ5sw@mail.gmail.com>



On 6/17/19 5:18 PM, Christoph Paasch wrote:
> 
> Hi Eric, I now have a packetdrill test that started failing (see
> below). Admittedly, a bit weird test with the SO_SNDBUF forced so low.
> 
> Nevertheless, previously this test would pass, now it stalls after the
> write() because tcp_fragment() returns -ENOMEM. Your commit-message
> mentions that this could trigger when one sets SO_SNDBUF low. But,
> here we have a complete stall of the connection and we never recover.
> 
> I don't know if we care about this, but there it is :-)

I guess it is WAI :)

Honestly I am not sure we want to add code just to allow these degenerated use cases.

Upstream kernels could check if rtx queue is empty or not, but this check will be not trivial to backport


Can you test :

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 00c01a01b547ec67c971dc25a74c9258563cf871..06576540133806222f43d4a9532c5a929a2965b0 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1296,7 +1296,8 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
        if (nsize < 0)
                nsize = 0;
 
-       if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf)) {
+       if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf &&
+                    !tcp_rtx_queue_empty(sk))) {
                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
                return -ENOMEM;
        }

  reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-17 17:03 [PATCH net 0/4] tcp: make sack processing more robust Eric Dumazet
2019-06-17 17:03 ` [PATCH net 1/4] tcp: limit payload size of sacked skbs Eric Dumazet
2019-06-17 17:14   ` Jonathan Lemon
2019-06-17 17:03 ` [PATCH net 2/4] tcp: tcp_fragment() should apply sane memory limits Eric Dumazet
2019-06-17 17:14   ` Jonathan Lemon
2019-06-18  0:18   ` Christoph Paasch
2019-06-18  2:28     ` Eric Dumazet [this message]
2019-06-18  3:19       ` Christoph Paasch
2019-06-18  3:44         ` Eric Dumazet
2019-06-18  3:53           ` Christoph Paasch
2019-06-18  4:08             ` Eric Dumazet
2019-07-10 18:23         ` Prout, Andrew - LLSC - MITLL
2019-07-10 18:28           ` Eric Dumazet
2019-07-10 18:53             ` Prout, Andrew - LLSC - MITLL
2019-07-10 19:26               ` Eric Dumazet
2019-07-11  7:28                 ` Christoph Paasch
2019-07-11  9:19                   ` Eric Dumazet
2019-07-11 18:26                     ` Michal Kubecek
2019-07-11 18:50                       ` Eric Dumazet
2019-07-11 10:18                   ` Eric Dumazet
2019-07-11 17:14                 ` Prout, Andrew - LLSC - MITLL
2019-07-11 18:28                   ` Eric Dumazet
2019-07-11 19:04                     ` Jonathan Lemon
2019-07-12  7:05                       ` Eric Dumazet
2019-07-16 15:13                   ` Prout, Andrew - LLSC - MITLL
2019-06-17 17:03 ` [PATCH net 3/4] tcp: add tcp_min_snd_mss sysctl Eric Dumazet
2019-06-17 17:15   ` Jonathan Lemon
2019-06-17 17:18   ` Tyler Hicks
2019-06-17 17:03 ` [PATCH net 4/4] tcp: enforce tcp_min_snd_mss in tcp_mtu_probing() Eric Dumazet
2019-06-17 17:16   ` Jonathan Lemon
2019-06-17 17:18   ` Tyler Hicks
2019-06-17 17:41 ` [PATCH net 0/4] tcp: make sack processing more robust David Miller
2019-08-02 19:02 [PATCH net 2/4] tcp: tcp_fragment() should apply sane memory limits Bernd
2019-08-02 19:14 ` Neal Cardwell
2019-08-02 19:58   ` Bernd
2019-08-14 14:41     ` Marcelo Ricardo Leitner

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